It is estimated that approximately one-third of all wastewater treatment facilities in the United States utilize a wastewater lagoon in some capacity during their treatment process. This means that there are more than 6,000 systems employing the use of wastewater lagoons in this country alone. That includes all fifty states, which translates to practically every American watershed, impacting the lives of millions of people nationwide. Lagoons, which can also be found in Canada and other parts of the world, became popular in the 1980's due to their simple design and low maintenance.
There are two different types of lagoon treatment processes, one known as a facultative or anaerobic lagoon and one aerated or aerobic lagoon. Facultative lagoon systems are typically comprised of several shallow ponds, 4-6 feet deep, with a typical overall retention time of 180 days. With the absence of oxygen, anaerobic bacteria break down the waste over a longer period of time. The clean effluent water can then be discharged either on a continuous basis or a periodic, controlled, basis. In controlled discharge systems, the water is stored in a separate storage lagoon and only discharged when water temperatures are likely to be warmer, typically spring (April and May) and fall (October and November) depending on the location of the facility and state regulations.
Aerated lagoons are typically deeper, 8-20 feet deep, and rely on either mechanical or diffused aeration for the supply of oxygen and mixing necessary to aerobically break down waste contaminants in the water. With typically 1-4 aeration cells, operated in series or parallel, aerobic lagoons generally have a retention time of anywhere between 20-40 days.
Properly designed lagoon systems can remove the common constituents found in a wastewater discharge permit, including Biochemical Oxygen Demand (BOD5) and Total Suspended Solids (TSS). However, water quality standards imposed by EPA in March 2006 have mandated State environmental regulators to begin imposing strict standards for ammonia (NH3-N), nitrite+nitrate, and total nitrogen (TN) discharge levels on all lagoon systems. This poses a problem for owners of lagoon systems as they were never designed with the intent of meeting stringent ammonia discharge limits.
For most lagoon owners, the existing options for meeting their new discharge permit are either to replace or radically change their entire facility. Many believe that replacing the wastewater lagoon with an advanced treatment system, such as a conventional activated sludge process, is the only way of achieving the lower discharge requirements. However, because advanced biological treatment processes are much more mechanical in their nature and require many more components that are both expensive to purchase and costly to install, this typically results in millions of dollars required for upfront capital costs even for the smallest of facilities. Moreover, with an increase in the amount of mechanical equipment, a facilities operation and maintenance budget often will double or triple in size. The average small community that operates lagoons today does not have large user base to spread these costs out over and, as a result, the cost of building and operating a mechanical treatment system is unfeasible. Indeed, for many of the small communities that still operate lagoon systems, this is undesirable today for many of the same reasons that such a mechanical treatment process was not originally selected: they do not have the financial wherewithal to either purchase or maintain and operate such a facility.
Accordingly, there is a need for a biological treatment process that is more cost effective from both a capital and operation cost perspective for existing lagoons to meet their new discharge requirements.